This invention relates to a vacuum container, and more particularly to a vacuum container hermetically sealed and kept at a high vacuum by absorbing gas produced in an envelope of the flat type by a getter.
A vacuum container kept at a high vacuum may be realized in the form of a field emission display (hereinafter referred to as "FED") in which field emission cathodes act as an electron source, by way of example. The FED includes an envelope formed by sealedly joining an anode substrate provided on an inner surface thereof with a display section including phosphors and a cathode substrate provided on an inner surface thereof opposite to the display section of the anode substrate with field emission cathodes to each other through an outer periphery thereof while spacing both substrates from each other at a predetermined interval.
In the FED thus constructed, the anode substrate on which the display section having the phosphors arranged at fine dot pitches is formed and the cathode substrate on which the field emission cathodes are formed each are made of a thin glass plate having a thickness as small as, for example, 2.5 mm and are spaced from each other at an interval as small as 0.2 mm, resulting in the envelope being highly reduced in thickness.
In order to ensure that the FED satisfactorily functions as a display device, it is required that the envelope constructed of the anode substrate and cathode substrate is kept at a high vacuum so as to permit the field emission cathodes to emit electrons with increased efficiency. For this purpose, it is generally constructed in such a manner that the envelope is evacuated to a vacuum as high as, for example, 10.sup.-6 Torr and gas remaining in the envelope is absorbed by a getter member to keep the envelope at a vacuum as high as, for example, 10.sup.-7 Torr.
In the conventional FED, as described above, the interval or gap defined between the anode substrate and the cathode substrate is reduced, to thereby render the envelope highly thin. Unfortunately, such a reduction in thickness of the envelope fails to permit the getter member for absorbing gas remaining in the envelope to be arranged in the envelope.
In order to address the problem, the conventional FED, as shown in FIG. 12 or 13, is so constructed that a getter box is arranged outside the envelope. The getter box has a getter film formed therein by deposition.
More particularly, the FED shown in each of FIGS. 12 and 13 includes an envelope 51 constituted by an anode substrate 52 which is formed on an inner surface thereof with a display section including anode conductors and phosphor layers and a cathode substrate 53 which is formed on an inner surface thereof with field emission cathodes. The anode substrate 52 and cathode substrate 53 are arranged so as to face each other while being positionally deviated from each other in a lateral direction of the envelope and are sealedly fixedly joined to each other through a spacer member 54 formed of an adhesive such as low-melting glass or the like arranged on an outer periphery of the substrates 52 and 53.
The envelope 51 has a side surface of which a part is removed. Also, the side surface of the envelope 51 is formed with an evacuation hole 55 which permits an interior of the envelope 51 communicate with an outside thereof therethrough. Reference numeral 56 designates a getter box which is fixed to a portion of the anode substrate positioned in proximity to the evacuation hole 55 and separate from the envelope 51 and the side surface of the envelope 51, resulting in a getter chamber 57 which communicates with the evacuation hole 55 being defined in the getter box 56.
The getter box 56 is formed with a though-hole 58 communicating with the evacuation hole 55. In the FED shown in FIG. 13, the getter box 56 formed with the through-hole 58 has an evacuation pipe 59 for evacuating the envelope therethrough formed at a portion of an outer surface of a portion thereof facing the cathode substrate 53. The FED shown in FIG. 13 has a plate-like metal lid 60 substituted for the evacuation pipe 59 shown in FIG. 12.
The getter box 56 is provided therein with a getter member 61, so that heating of the getter member 61 leads to vaporization of the getter member, to thereby permit a getter firm to be depositedly formed on an inner surface of the getter chamber 57. This results in the thus-formed getter firm absorbing gas which remains in the envelope 51, to thereby keep the envelope 51 at a vacuum as high as, for example, 10.sup.-7 Torr.
Thus, in the conventional FED shown in each of FIGS. 12 and 13, the getter box 56 is arranged separate from the envelope 51 in a manner to be projected outside the cathode substrate 53 constituting a part of the envelope 51. Unfortunately, such arrangement of the getter box 56 causes a thickness of the FED to be increased by an amount corresponding to a thickness of the getter box 56, so that the thickness-reduced FED fails to exhibit its intrinsic advantage owing to a reduction in thickness thereof. More specifically, the envelope 51 is formed into a thickness of 2.5 mm, whereas the getter box is formed into a thickness as large as 7 mm.
Also, the getter box 56 is arranged in a manner to extend between the anode substrate 52 and the cathode substrate 53 which are positionally deviated from each other, so that a closed space communicating with the evacuation hole 55 of the envelope 51 may be formed therein. This renders a configuration of the FED complicated, renders processing or working thereof troublesome and causes an increase in manufacturing cost thereof.
Further, evacuation of the envelope 51 gives rise to outward discharge of gas in the envelope 51 through the evacuation hole 55, as well as through the getter box 56 projected from the envelope 51, so that an evacuation path length is substantially increased due to arrangement of the getter box 56 outside the envelope 51. This results in a flow resistance of the gas occurring during the evacuation being increased, so that much time is required for evacuating the envelope 51 to a high vacuum desired.